An appropriate ventilation system supplies each intended site with adequate fresh air, provides suitable temperature and humidity, maintains good air conditions using ventilation power in the most economical way, in order to ensure the safety of workers and improve the environment. The appropriate ventilation system features a simple structure and a suitably designed configuration for the purpose of safe production. The property of the ventilation apparatus has a very important influence on ventilation effect.
The majority of the existing ventilation apparatus with counter-rotating impellers adopts two stage impellers which are driven by two motors rotating in opposite directions, respectively. The main problems are as follows: 1) the motor and the impeller are directly coupled to each other and fixed inside the air duct, the heat dissipation of the motor in the air duct is worse as compared to that in the atmosphere, and it is inconvenient to repair the motor; and 2) in the small and medium-sized coal mines or in the early stage of the excavation for large tunnel, the requirement on ventilation pressure is relatively low, and thus the high pressure ventilation generated by the counter-rotating impellers can cause energy waste in this case. For example, publication No. CN101403389A discloses “a counter-rotating axial flow fan” including an electric motor, an air duct, two stage impellers, a gearbox and bevel gears. The motor drive is disposed inside the air duct. The counter rotation of the two stage impellers is achieved by the driving of the bevel gears in the gearbox. The arrangement of the gearbox inside the air duct causes the inconvenience of maintenance and operation of the apparatus and constraints the axial distance between the two stage impellers, and hence is not suitable for the counter rotating type of ventilation apparatus requiring a compact structure.
A prior art involving an external motor is for example disclosed in publication No. CN2777255 relating to “a counter-rotating type of axial flow ventilator with external motor” including two motors, a long shaft, two stage impellers and diffusers. The two motors are placed outside the air duct and drive the two stage impellers respectively through the transmission of the long shaft connected thereto. The system powered by two motors will occupy a larger floor area as compared to that powered by a single motor, and thus is inconvenient to operate.
As a further example, publication No. CN2793377 discloses “a two-stage counter-rotating axial flow fan” which comprises a motor, a universal coupler, a fairing, two stage impellers, a gear transmission mechanism with dual output shafts and a diffuser. In operation, the motor drives the gear transmission mechanism with dual output shafts through the universal coupler, and the mechanism in turn drives the two stage impellers to rotate reversely. When only a small ventilation pressure is required, the high pressure produced by the ventilation apparatus with counter-rotating impellers due to the synchronous rotation of the two impellers will cause a great energy waste.
Therefore, it is very important to develop a ventilation apparatus with counter-rotating impellers driven by long shaft that has a more compact structure, is easy for maintenance and operation and is switchable between single impeller rotation and counter rotation of two impellers to save energy.